Pore Diameter Of Support Research Articles

Towards a Correlation Between Iron/Cobalt Content, Support Pore Size and Metal Particle Size in Supported Catalysts

AbstractFe−Co‐based catalysts supported on γ‐Al2O3, Aerosil 200 silica and zeolite 4A were prepared by co‐precipitation of the respective nitrates in the presence of ammonium hydroxide. The objective was to demonstrate the influence of Fe/Co mass ratio and support pore size on metal particle size. Catalysts were characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), N2 physisorption, Fourier‐transformed infrared spectroscopy (FTIR), and scanning (SEM) and transmission (TEM) microscopies. It was demonstrated that the minimal presence of Fe was enough to reduce the average particle diameters by half. Increasing Fe content did not cause proportional decreases in the average particle diameter. The support pore diameter probably played a role in the crystallization step of bimetallic and Fe monometallic catalysts, whose particle diameters were similar to those observed for the pores. This phenomenon was not observed for Co monometallic catalysts.

Effect of pore diameter and structure of mesoporous sieve supported catalysts on hydrodesulfurization performance

A series of mesoporous sieves with different pore diameters and structures have been controllably synthesized by adding variable amounts of swelling agent 1,3,5-trimethylbenzene in the preparation process for SBA-15. NiMo catalysts supported by mesoporous sieves are prepared by using the newly proposed Mo-based organic–inorganic hybrid nanocrystals as precursors to load Mo and subsequently using wetness impregnation to load Ni. The hydrodesulfurization (HDS) activity of these obtained catalysts is evaluated in a continuously flowing tubular fixed-bed microreactor using 1wt% dibenzothiophene (DBT) in heptane as a model compound. The results show that HDS ratio has gradually increased as the pore diameter of supports is enlarged from 7 to 11nm with the mesostructure keeping an ordered two-dimensional hexagonal symmetry. When the structure is in the intermediate stage of structural transition from ordered hexagonal mesostructure to mesocecullar structure, HDS ratio is decreased dramatically due to the disordered and collapsed structure to block the pore channels. After the mesocecullar structure with three-dimensional open pore channels is formed which is more convenient for the molecular diffusion, HDS ratio has increased again as a result. It is concluded that both the pore size and window size connecting the adjacent pores play an important role in the HDS activity but the window size is of more significant importance, which is the key point for the enhanced catalytic performance.

First time investigation of Pt nanocatalysts deposited inside carbon mesopores of controlled length and diameter

This work represents the first-reported synthesis and evaluation of Pt-loaded colloid-imprinted carbon (CIC) supports consisting of a porous shell surrounding a solid core, for use as catalysts for cathodes in proton exchange membrane fuel cells (PEMFCs). Increasing the temperature of imprinting during the synthesis of CIC supports, from 250 to 400 °C, gave a five times increase in porous shell thickness (average pore depth), as confirmed by gas sorption and transmission electron microscopy studies. The CIC supports, all with a 26 nm pore diameter, were loaded with 20 wt% Pt and characterized with 3D transmission electron microscopy and electron tomography, showing that the Pt nanoparticles are uniformly deposited throughout the CIC pores. Using 3-electrode electrochemistry in 0.5 M H2SO4, it was found that the rate (per active Pt surface area) of the oxygen reduction reaction is independent of the pore length, with no transport limitations encountered. This demonstrates that full utilization of both the Pt and the CIC internal surface area was achieved under these experimental conditions, which promises benefits in terms of enhanced Pt utilization, thus lowering the cost and improving the durability of PEMFCs. Furthermore, this work has opened up an entirely new direction for fuel cell catalyst layer design by allowing the controlled modification of both carbon support pore diameter and pore length, also of relevance for battery and capacitor applications.

Combining confinement and NO calcination to arrive at highly dispersed supported nickel and cobalt oxide catalysts with a tunable particle size

Control over the size and size distribution of supported nanoparticles is key to their efficient use in catalysis. In the preparation of nanoparticles by impregnation using nitrate precursors, the support pore diameter can be used to influence the average crystallite size. However, the particle size distributions obtained via this method are generally broad and the dispersions relatively low. Higher dispersions and narrow particle size distributions are obtained via thermal decomposition of the metal nitrate precursor in 1% (v/v) NO in Ar instead of air. Here we will show that by combining the confinement effect of ordered mesoporous silica with a decomposition step of metal nitrates in NO, silica supported nickel and cobalt oxides with a tunable particle size (2–4 nm) can be obtained at high loadings (10–20 wt%).

Cobalt supported on alumina and silica-doped alumina: Catalyst structure and catalytic performance in Fischer–Tropsch synthesis

The paper addresses the structure and catalytic performance in fixed bed reactor at 20 bars of cobalt Fischer–Tropsch catalysts supported by commercial alumina (Puralox) and silica-doped alumina (Siralox). The cobalt loading varied between 8 and 15 wt.%; both alumina and silica-doped alumina supports had similar textural properties. Cobalt dispersion in both supports was principally affected by support pore diameter; at high cobalt loadings, cobalt particle size slightly increased with cobalt content. The presence of small amounts of silica in alumina (5 wt.% SiO2) enhanced cobalt reducibility and hindered formation of hardly reducible cobalt aluminate species. Higher Fischer–Tropsch reaction rate over cobalt catalysts supported on silica-doped alumina was attributed to a better cobalt reducibility. Cet article porte sur la structure et les performances catalytiques dans un réacteur à lit fixe des catalyseurs Fischer–Tropsch à base de cobalt supportés par alumine (Puralox) ou par alumine dopée au silicium (Siralox). Le taux de cobalt varie entre 8 et 15% en poids; les deux supports présentent des caractéristiques texturales proches. Il a été constaté que la dispersion du cobalt était principalement influencée par le diamètre des pores. Par ailleurs, à des teneurs élevées en cobalt, la taille des particules d'oxyde de cobalt tend à augmenter légèrement avec la teneur en métal. La présence de silice dans l'alumine (5% poids de SiO2) améliorerait la réductibilité du cobalt et empêcherait la formation de phases d'aluminate de cobalt inactives en synthèse Fischer–Tropsch. Les catalyseurs qui contiennent de la silice ont montré une vitesse de réaction plus importante. Ceci a été attribué à une meilleure réductibilité du cobalt.

Fischer–Tropsch synthesis over un-promoted and Re-promoted γ-Al 2O 3 supported cobalt catalysts with different pore sizes

The effect of rhenium on the Fischer–Tropsch synthesis activity and selectivity of γ-Al 2O 3 supported cobalt catalysts was investigated in fixed-bed reactors at T = 483 K, P = 20 bar, and H 2/CO = 2.0. Catalysts containing 20 wt.% cobalt and 0 or 0.5 wt.% rhenium were prepared by incipient wetness impregnation of different γ-Al 2O 3 supports with aqueous solutions of cobalt nitrate hexahydrate and for the Re-promoted catalysts, also perrhenic acid. The γ-Al 2O 3 supports had very different pore characteristics. The post-calcination Co 3O 4 crystallite size was predominantly controlled by the γ-Al 2O 3 support pore diameter. Presence of Re had only a minor effect on the crystallite size. For all catalysts, supported Co 3O 4 was reduced in two steps to Co 0 with CoO as intermediate species. However, while reduction of Co 3O 4 to CoO took place in the same temperature range for all catalysts, the reduction temperature of CoO to Co 0 was dependent on the catalyst properties. Large particles present in wide pores were easier to reduce than small particles located in narrow pores. In addition, Re promoted the reduction of CoO. The effect of rhenium as a reduction promoter was less pronounced at increasing pore size and particle size. Re also had a similar positive impact on the cobalt dispersion of the catalysts. Although Re significantly increased the Fischer–Tropsch synthesis cobalt-time yield, it did not modify the site-time yield. The deactivation rates of all the catalysts were also similar up to 100 h on stream. Positive correlations were found between the catalyst pore diameter and the C 5+ selectivity and between the cobalt particle size and the C 5+ selectivity. Re had a consistent positive, albeit small, effect on the C 5+ selectivity.

Effects of Porous Polystyrene Resin Parameters onCandida antarcticaLipase B Adsorption, Distribution, and Polyester Synthesis Activity

Polystyrene resins with varied particle sizes (35 to 350-600 microm) and pore diameters (300-1000 A) were employed to study the effects of immobilization resin particle size and pore diameter on Candida antarctica Lipase B (CALB) loading, distribution within resins, fraction of active sites, and catalytic properties for polyester synthesis. CALB adsorbed rapidly (saturation time </= 4 min) for particle sizes </= 120 microm (pore size = 300 A). Infrared microspectroscopy showed that CALB forms protein loading fronts regardless of resin particle size at similar enzyme loadings ( approximately 8%). From the IR images, the fractions of total surface area available to the enzyme are 21, 33, 35, 37, and 88% for particle sizes 350-600, 120, 75, 35 microm (pore size 300 A), and 35 microm (pore size 1000 A), respectively. Titration with methyl p-nitrophenyl n-hexylphosphate (MNPHP) showed that the fraction of active CALB molecules adsorbed onto resins was approximately 60%. The fraction of active CALB molecules was invariable as a function of resin particle and pore size. At approximately 8% (w/w) CALB loading, by increasing the immobilization support pore diameter from 300 to 1000 A, the turnover frequency (TOF) of epsilon-caprolactone (epsilon-CL) to polyester increased from 12.4 to 28.2 s-1. However, the epsilon-CL conversion rate was not influenced by changes in resin particle size. Similar trends were observed for condensation polymerizations between 1,8-octanediol and adipic acid. The results herein are compared to those obtained with a similar series of methyl methacrylate resins, where variations in particle size largely affected CALB distribution within resins and catalyst activity for polyester synthesis.

Contributions of heterogeneous and homogeneous chemistry in the catalytic partial oxidation of octane isomers and mixtures on rhodium coated foams

Catalytic partial oxidation experiments with n-octane, 2,2,4-trimethylpentane ( i-octane), and an n-octane: i-octane (1:1) mixture were performed on 80 and 45 ppi Rh-coated α -alumina foam supports at 2, 4, and 6 SLPM total flow rate in order to explore the effects of chemical structure for single components and binary mixtures on fuel reactivity and product distribution. When reacted as single components, the conversion of i-octane is greater than n-octane at C / O > 1.1 (both fuel conversions are 100% for C / O < 1.1 ). However, when reacted in an equimolar mixture, the conversion of n-octane is greater than i-octane. All three fuels give high selectivity to syngas ( H 2 and CO) on 80 ppi supports for C / O < 1 . For C / O > 1 , n-octane produces high selectivity to ethylene while i-octane makes i-butylene and almost no ethylene. The fuel mixture produces these species proportional to the mole fractions of n-octane and i-octane within the reacting mixture. Increasing the support pore diameter decreases the selectivity to syngas and increases H 2 O and olefin selectivity. The reforming of all three fuels is modeled using detailed chemistry by decoupling the heterogeneous and homogeneous chemistry in a two-zone plug flow model. Detailed homogeneous reaction mechanisms with several thousand elementary reactions steps and several hundred species are used to simulate experimentally observed olefin selectivities for all three fuels on 80 and 45 ppi monoliths at 2, 4, and 6 SLPM quite well. These results support the hypothesis that a majority of the observed olefins are made through gas-phase chemistry.

Fischer–Tropsch synthesis over silica supported cobalt catalysts: mesoporous structure versus cobalt surface density

The effect of support mesoporous structure and cobalt content on cobalt dispersion and reducibility was studied using two series of Fischer–Tropsch (FT) silica supported cobalt catalysts. The first series of the catalysts was supported by an SBA-15 periodic mesoporous silica with narrow pore size distribution, the second series was supported by a commercial mesoporous silica with broader pore size distribution. It was shown that in a wide range of cobalt surface densities (0–50 Co/nm 2), cobalt dispersion in silica supported catalysts was largely influenced by support texture. Cobalt dispersion was higher in Co catalysts supported by the SBA-15 silica with a pore diameter of 9.1 nm than in the commercial mesoporous silica with an average pore diameter of 33 nm. A more than 10-fold increase in cobalt surface density did not result in any noticeable sintering of Co 3O 4 particles in SBA-15 periodic mesoporous silicas; the cobalt dispersion seems to be maintained by catalyst mesoporous structure. The effect of support pore diameter on cobalt dispersion was less significant for the catalysts supported by commercial silicas with broader pore size distribution. At the range of cobalt surface densities from 5 to 15 Co/nm 2, higher Fischer–Tropsch reaction rates were observed over cobalt catalysts supported by the SBA-15 periodic mesoporous silica. This effect was attributed to higher cobalt dispersion in these catalysts. An increase in cobalt surface densities did lead to any significant changes in hydrocarbon selectivities and in chain growth probabilities for both series of supported catalysts.

The adsorption and decomposition of cyanogen chloride by modified inorganic molecular sieves

Aluminosilicate and silicate porous solids have been evaluated as supports for triethylenediamine (TEDA) for the adsorption and decomposition of cyanogen chloride. A series of silica-gel supports has been used to study the effect of varying pore size. A series of faujasitic zeolites has been used to examine the effect of the cation exchange capacity of the support and the type of exchangeable cation. Results show that the activity of adsorbed TEDA towards cyanogen chloride appears to increase with increasing support pore diameter, and TEDA seems to be activated by basic adsorption sites on the support. Cesium-exchanged zeolite supports are particularly active. In general, zeolite supports appear to confer significantly higher activity to TEDA than traditional activated carbon supports. A series of mesoporous MCM-41 and AlMCM-41 supports has also been studied, but the activities of adsorbed TEDA are lower than expected. Significantly, the specific surface area of the inorganic supports does not seem to be a primary factor in controlling adsorbed TEDA activity.

Effect of the Porous Structure of the Support and Modifying Cation on the Catalytic Properties of the Co/SiO 2 ·M n + System in the Hydrogenation of Carbon Monoxide to Give Hydrocarbons

Data are given on the activity and selectivity of formation of C5+ hydrocarbons in the Fischer–Tropsch synthesis depending on mean diameter of support pores (1.6-907 nm). The formation of C5+ hydrocarbons was found to be a function of the mean support pore diameter. The optimal value was 8-12.6 nm. The output and selectivity of formation of the hydrocarbons are also functions of the introduced cation.

Grafting of Molecularly Imprinted Polymer Films on Silica Supports Containing Surface-Bound Free Radical Initiators

Silica particles containing surface-bound free radical initiators have been used as supports for the grafting of thin films of molecularly imprinted polymers (MIPs). This technique offers a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity in chromatographic or sensor applications. Thus prepared MIPs imprinted with l-phenylalanine anilide, have been characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), elemental analysis, fluorescence microscopy, and scanning electron microscopy (SEM), providing evidence concerning the reproducibility in each step and the quantity and quality of the grafted films. The chromatographic properties of the materials have been investigated with respect to the average layer thickness of the polymer on the surface, the solvent, the support pore diameter, the cross-linker concentration, and the composition of the mobile phase. For the porous particles, the column efficiency depended strongly on the amount of grafted polymer. Thus, polymers grafted as thin films (ca. 0.8 nm as average film thickness) on silica with 10 nm average pore diameter showed the highest column efficiency giving plate numbers (N) for the imprinted enantiomer of ca. 700 m-1 and for the antipode ca. 24 000 m-1. This resulted in baseline resolutions on a 33 mm long column in less than 5min. On the other hand the sample load capacity and separation factor increased up to 7.0 nm layer thickness and dropped again for larger amounts of grafted polymer. A support with an average pore diameter of 100 nm and a 3.8 nm layer thickness showed a far higher saturation capacity than values previously determined for the conventional monolithic materials.

Silica supported cobalt Fischer–Tropsch catalysts: effect of pore diameter of support

The influence of the effect of average pore diameter of silica support on the physical and chemical properties of supported cobalt catalysts and their performance in the Fischer–Tropsch synthesis was investigated. Silicas with different mean pore diameter (20, 40, 60, 100 and 150 Å) were impregnated with cobalt nitrate to produce catalysts containing 20 wt.% cobalt. The metal crystallite size and degree of reduction was found to increase with increasing pore diameter of the support for supports with an average pore diameter larger or equal to 40 Å, and hence the dispersion decreased. In impregnated catalysts, the metal crystallites seems to appear in clusters on the support. With increasing average pore diameter, the size of these clusters increases. In the Fischer–Tropsch synthesis, the 100 Å supported catalyst proved to be the most active and selective catalyst for hydrocarbon formation. The C 5+ and methane selectivity passed through a maximum and minimum at the 100 Å supported catalyst, respectively, which can be explained quantitatively using the reactant transport model proposed by Iglesia et al.

Variables in the high-performance anion-exchange chromatography of proteins

The effect of mobile phase velocity, separation time, support pore diameter, column length, and temperature on resolution and loading capacity of a new commercially available high-performance anion-exchange support, SynChropak AX-300, has been examined. This material is a macroporous spherical silica of 10 μm particle size with a bonded polymeric amine layer. It was found that the heterogeneity of ovalbumin samples, combined with bovine serum albumin, make them useful probes in evaluation of anion-exchange supports. In the columns of 4.1 mm i.d., the highest resolutions of proteins were achieved at a flow rate of 0.25 ml/min. Up to 10 mg of protein per injection could be applied on a 4.1 × 250 mm AX-300 column with good resolution. Columns of 50 mm length had one-tenth the protein load capacity of a 250-mm column, retaining approximately 75% of the resolution.

Glycerolpropylsilane bonded phases in the steric exclusion chromatography of biological macromolecules.

Glycerolpropylsilane bonded phases have been found to control the adsorption and/or denaturation of proteins and nucleic acids on controlled porosity glass supports. The bonded-phase thickness is 18-19A while the amount of glycerol moiety varies from 80 to 150 mumoles/g depending on support pore diameter. It has been demonstrated that carbohydrate bonded supports may be used in the chromatography of proteins, nucleic acids, and polysaccharides.